Heatable hoses or tubes have been used to transport hot gases to and from exit stacks without cooling the gas to below the dew point. Depending on the end-use requirements of these hoses, a variety of tubes have been used in the past to make the hoses. Commonly, the tube is made of a metal, such as stainless steel, providing the hose with a great deal of strength and chemical resistance. However, hoses having metal tubes, while readily available and reasonably inexpensive, are heavy and not very flexible.
Polymeric tubes are also known in the art. The polymeric tubes commonly used in heatable hoses are made of fluoro, polymers such as polytetrafluoroethylene (PTFE), copolymers of tetrafluoroethylene and perfluoro(propyl vinyl ether) (PFA) or fluorinated ethylene propylene copolymer (FEP). These fluoropolymers are fairly heat stable and exhibit a lower weight per unit length for a certain thickness tube than a comparable metal tube. Fluoropolymer tubes are also relatively flexible when compared to metal tubes of comparable sizes and shapes. However, hoses containing fluoropolymer tubes typically do not possess as much high strength as comparable hose containing a metal tube. This is of concern if the hose is of an extended length and is required to support its own weight. The strength of the fluoropolymer tube may be adversely effected by temperatures at which the hose may be heated. Also, fluoropolymer tubes exhibit a measure of permeation to certain gases, particularly acid gases such as NO.sub.x and SO.sub.x. This is of concern when a hose containing a fluoropolymer tube is part of a gas sampling device attached to a emitting stack for the detection and measurement of acid gases.
It would be desirable to have a flexible heatable hose comprising a polymedic tube that is relatively light, relatively strong, relatively flexible and is relatively impermeable to many gases, even at elevated temperatures.